Summary of significant accounting policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2013 Y
Significant Accounting Policies [Line Items]
Estimated service life of the asset refineries, in years	25
Estimated service life of other major assets, in years	20
Amortization of computer software development costs, in years	15
Amortization of customer lists, in years	10 years
Maximum
Significant Accounting Policies [Line Items]
Investments in mining and transportation systems at oil sands mining properties, useful life	15 years
Syncrude Joint Venture
Significant Accounting Policies [Line Items]
Undivided interest in oil and gas activities	25.00%
Kearl Project
Significant Accounting Policies [Line Items]
Undivided interest in oil and gas activities	70.96%